Because the adverse reactions associated with treatment of onchocerciasis, loiasis, and lymphatic filariasis can be severe, systemic, and debilitating the mediators of this posttreatment reaction have been identified and quantified. In the acute phase (first 48 hours) an intracellular Wolbachia endosymbiont appears in the bloostream and is correlated with the presence of the inflmmatory mediators of the posttreatment adverse reactions. Later, the eosinophil plays a major role as do the chemokines associated with eosinophil trafficking.